Catalyst and method for hydrogenating aromatic compounds

ABSTRACT

The invention relates to the hydrogenation of aromatic compounds, in particular the preparation of alicyclic polycarboxylic acids or esters of these, via ring hydrogenation of the corresponding aromatic polycarboxylic acids or esters of these, and also to catalysts suitable for this purpose.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a national stage application of International PatentApplication No. PCT/EP03/04386, filed on Apr. 26, 2003, and claimspriority to German Patent Application No. 102 25 565.2, filed on Jun.10, 2002, both of which are incorporated herein by reference in theirentireties.

The invention relates to the hydrogenation of aromatic compounds, inparticular the preparation of alicyclic polycarboxylic acids or estersof these, by ring hydrogenation of the corresponding aromaticpolycarboxylic acids or esters of these, and also to catalysts suitablefor this purpose.

Alicyclic polycarboxylic esters, such as the esters ofcyclohexane-1,2-dicarboxylic acid, are used as a component oflubricating oil and as auxiliaries in metalworking. They are also usedas plasticizers for polyolefins and for PVC.

For plasticizing PVC it is currently mainly esters of phthalic acid thatare used, for example dibutyl, dioctyl, dinonyl, or didecyl esters.Recently, there has been increasing controversy about the use of thesephthalates, and therefore there is a risk that their use in plasticscould become restricted. Alicyclic polycarboxylic esters, some of whichhave been described in the literature as plasticizers for plastics,could then be available as suitable replacements.

The most economic route to preparation of alicyclic polycarboxylicesters in most cases is ring hydrogenation of the corresponding aromaticpolycarboxylic esters, for example of the abovementioned phthalates.Some processes for this purpose have been disclosed:

U.S. Pat. No. 5,286,898 and U.S. Pat. No. 5,319,129 describe a processwhich can hydrogenate dimethyl terephthalate on supported Pd catalystsdoped with Ni or with Pt and/or with Ru, at temperatures of 140° C. orabove and at a pressure of from 50 to 170 bar, to give the correspondingdimethyl hexahydroterephthalate.

U.S. Pat. No. 3,027,398 discloses the hydrogenation of dimethylterephthalate on supported Ru catalysts from 110 to 140° C. and from 35to 105 bar.

DE 28 23 165 hydrogenates aromatic carboxylic esters on supported Ni,Ru, Rh, and/or Pd catalysts, to give the corresponding alicycliccarboxylic esters at from 70 to 250° C. and from 30 to 200 bar. Amacroporous support is used here, with an average pore size of 70 nm anda BET surface area of about 30 m²/g.

WO 99/32427 and WO 00/78704 disclose processes for hydrogenatingbenzenepolycarboxylic esters to give the corresponding alicycliccompounds. Here, use is made of supported catalysts which comprise ametal of the 8th transition group alone or together with at least onemetal of the 1st or 7th transition group of the periodic table, andwhich have macropores. Ruthenium is used as the preferred metal of the8th transition group. For the hydrogenation, use is made of threedifferent types of catalyst which differ substantially in their averagepore diameter and their BET surface areas.

-   Catalyst I: average pore diameter greater than 50 nm and BET surface    area smaller than 30 m²/g-   Catalyst II: average pore diameter from 5 to 20 nm and BET surface    area greater than 50 m² μg-   Catalyst III: average pore diameter greater than 100 nm and BET    surface area smaller than 15 m²/g

The catalysts used for ring-hydrogenating aromatic carboxylic acids oresters of these are intended to permit a high reaction rate, generateonly a small proportion of by-products, and have a long operating time.

The activity and selectivity of hydrogenation catalysts depend on theirsurface properties, such as pore size, BET surface area, or surfaceconcentration of the active metals.

In a continuously operated process, a catalyst is then exposed tomechanical, thermal, and chemical stresses which alter the pore size orthe BET surface area and therefore reduce the activity and selectivityof this catalyst.

For example, many catalysts are found to exhibit not only mechanicalabrasion but also enlargement of pore volumes and diameter through acidetching.

Aromatic polycarboxylic esters often comprise small amounts ofcarboxylic acids, and traces of acid are also produced during the ringhydrogenation of esters. Partial esters of polycarboxylic acids, orpolycarboxylic acids themselves, are acidic by virtue of theirstructure. This means that a hydrogenation catalyst suitable for acontinuous process should be resistant to acid under the conditions ofhydrogenation, even at relatively high temperatures.

The known catalysts do not yet fulfill the desired requirements inrelation to activity, selectivity, or stability. For example, it isknown that, unlike α-Al₂O₃, γ-Al₂O₃ is insufficiently resistant to acid.

An object was therefore to develop the catalysts for ring-hydrogenatingaromatic carboxylic acids and/or esters of these, with improved propertyprofiles.

Surprisingly, it has now been found that catalysts which comprise atleast one metal of the eighth transition group and are composed of asupport material with an average pore diameter of from 25 to 50 nm andwith a specific surface area greater than 30 m²/g hydrogenate aromaticcarboxylic acids and/or esters of these (full esters or partial esters)with high selectivity and space-time yield to give the correspondingalicyclic polycarboxylic acids or esters of these, without significantside reactions.

The present invention therefore provides a catalyst for hydrogenatingaromatic compounds to give the corresponding alicyclic compounds, whichcomprises at least one metal of the eighth transition group of theperiodic table on or in a support material, where the support materialhas an average pore diameter of from 25 to 50 nm and a specific surfacearea greater than 30 m²/g.

Catalysts of this type may in particular be used for hydrogenatingaromatic compounds. The present invention also provides a process forcatalytically hydrogenating aromatic compounds, usinghydrogen-containing gases on a catalyst which comprises at least onemetal of the eighth transition group of the periodic table on or in asupport material, where the support material has an average porediameter of from 25 to 50 nm and a specific surface area greater than 30m²/g.

In principle, the catalysts may comprise any of the metals of the eighthtransition group of the periodic table. The active metals preferablyused are platinum, rhodium, palladium, cobalt, nickel, or ruthenium, ora mixture of two or more of these, and ruthenium in particular is usedhere as active metal.

Besides the abovementioned metals, there may be at least one metal ofthe first and/or seventh transition group of the periodic table of theelements present in the catalysts. It is preferable to use rheniumand/or copper.

The content of the active metals, i.e. of the metals of the first and/orseventh and/or eighth transition group, is generally from 0.1 to 30% byweight. The precious metal content, i.e. content of the metals of theeighth transition group (more specifically: of the fifth and sixthperiod), calculated in terms of metal, in the range from 0.1 to 10% byweight, in particular in the range from 0.8 to 5% by weight, veryparticularly from 1 to 3% by weight.

To prepare the catalyst of the invention, use is made of supportmaterials with an average pore diameter in the range from 25 to 50 nm(the average pore diameter is determined by Hg porosimetry, inparticular to DIN 66133.)

In the support materials used a distinction may be made betweenmicropores (pore diameter smaller than 2 nm), mesopores (pore diameterfrom 2 to 50 nm), and macropores (pore diameter greater than 50 nm). Forinstance, it is possible to use support materials with the followingcombinations of pore type.

-   a) only mesopores-   b) micropores and mesopores-   c) mesopores and macropores-   d) micropores and mesopores, and macropores-   e) micropores and macropores

A decisive factor for preparing the catalyst of the invention is that,irrespective of the pore size distribution, the average pore diameter ofthe support material is from 25 to 50 nm. The average pore diameter ispreferably from 25 to 40 nm, very particularly preferably from 30 to 40nm.

It is therefore also possible to use support materials with highmacropore content (>550%) as long as the average pore diameter is from25 to 50 nm, preferably from 25 to 40 nm, very particularly preferablyfrom 30 to 40 nm.

The specific surface area of the support (determined by the BET methodby nitrogen adsorption to DIN 66131 is greater than 30 m² g, and thespecific surface area is preferably from 30 to 90 m²/g or from 35 to 90m²/g, in particular from 40 to 60 m²/g.

In one specific embodiment of the invention, the support materials usedto prepare the catalysts comprise those in which over 90%, in particularover 95%, of the total pore volume is made up by micro- and mesopores,i.e. by pores with a diameter of from 0.1 to 50 nm, preferably from 0.1to 20 nm.

The supports used for preparing the catalysts of the invention comprisesolids whose average pore diameter and whose specific surface area liewithin the ranges mentioned. Examples of substances which may be used assupport are the following: activated carbon, silicon carbide, aluminumoxide, silicon oxide, aluminosilicate, titanium dioxide, zirconiumdioxide, magnesium oxide, and/or zinc oxide, or a mixture of these.

To prepare the catalysts of the invention it is preferable to usesupports which are resistant to carboxylic acids under the conditions ofhydrogenation. Examples of these are activated carbon, silicon carbide,silicon dioxide, titanium dioxide, and/or zirconium dioxide, andmixtures of these compounds.

The support materials used very particularly preferably comprisetitanium dioxides. Titanium dioxide occurs in three forms (anatase,rutile, brookite), of which anatase and rutile are the commonest. Toprepare the catalysts of the invention, use may be made of any of theforms of titanium dioxide, or titanium dioxides in which at least twoforms are present alongside one another, or a mixture of varioustitanium dioxides, if their average pore diameter and specific surfacearea are within the range of the invention. A preferred support materialis Aerolyst 7711® (product marketed by Degussa AG, Düsseldorf, Germany).This support is composed of from 15 to 20% by weight of rutile and from80 to 85% by weight of anatase. Examples of other titanium dioxidesupports which are suitable for preparing the catalysts of the inventionare supports prepared from titanium oxides from a sulfuric acid process.They generally comprise >98% of anatase.

The catalysts of the invention may be obtained by applying at least onemetal of the eighth transition group of the periodic table and, whereappropriate, at least one metal of the first and/or seventh transitiongroup of the periodic table, to a suitable support. It is also possiblefor the active metals and the support to be prepared simultaneously,i.e. it is possible to use a bulk catalyst.

The application method may be impregnation of the support in aqueousmetal salt solutions, e.g. aqueous ruthenium salt solutions,spray-application of appropriate metal salt solutions onto the support,or any other suitable method. Suitable metal salts of the first,seventh, or eighth transition group of the periodic table are thenitrates, nitrosyl nitrates, halides, carbonates, carboxylates,acetylacetonates, chloro complexes, nitrito complexes, or aminecomplexes of the appropriate metals, preference being given to thenitrates and nitrosyl nitrates.

In the case of catalysts which comprise not only the metal of the eighthtransition group of the periodic table but also other metals applied asactive metal, the metal salts or metal salt solutions may be appliedsimultaneously or in succession.

The supports impregnated or coated with metal salt solution are thendried, preferably at temperatures of from 80 to 150° C., and optionallycalcined at temperatures of from 200 to 600° C. In the event of separateimpregnation application, the catalyst is dried after each impregnationstep and optionally calcined, as described above. There is norestriction here on the sequence in which the active components areapplied.

The application of the active component(s), drying, and calcination mayoptionally take place in a single operation, for example byspray-application of an aqueous metal salt solution to the support attemperatures above 200° C.

It is essential that the catalysts of the invention are converted to aform which has low flow-resistance during the hydrogenation process,examples being tablets, cylinders, extrudates, and rings. Various pointsin the catalyst preparation process here may be chosen for the shapingprocess.

In the process of the invention, the hydrogenation is carried out in theliquid phase or gas phase. The hydrogenation may be carried outbatchwise or continuously on suspended catalysts or particulatecatalysts in a fixed bed. In the process of the invention preference isgiven to continuous hydrogenation on a fixed-bed arrangement ofcatalysts where the product/starting material phase is primarily in theliquid state under the conditions of the reaction.

If the hydrogenation is carried out continuously on a catalyst arrangedin a fixed bed, it is advantageous to convert the catalyst into theactive form prior to the hydrogenation. This may be achieved byreduction of the catalyst using hydrogen-containing gases, following atemperature program. This reduction may, where appropriate, be carriedout in the presence of a liquid phase which trickles over the catalyst.The liquid phase used here may comprise a solvent or the hydrogenationproduct.

Differing versions of the process of the invention may be selected. Itcan be carried out adiabatically, polytropically, or practicallyisothermally, i.e. with a temperature rise typically smaller than 10°C., in one or more stages. In the latter case it is possible to operateall of the reactors, advantageously tubular reactors, adiabatically orpractically isothermally, or else to operate one or more adiabaticallyand the others practically isothermally. It is also possible tohydrogenate the aromatic compounds in a straight pass or with productreturn.

The process of the invention is carried out in the mixed liquid/gasphase or liquid phase, cocurrently in three-phase reactors, thehydrogenation gas being distributed in a manner known per se within theliquid starting material/product stream. To promote uniform liquiddistribution, improved dissipation of the heat of reaction, and highspace-time yield, the reactors are preferably operated with high liquidflow rates of from 15 to 120, in particular from 25 to 80, m³ per m² ofcross section of the empty reactor per hour. If the reactor is operatedwith a straight pass, the liquid hourly space velocity (LHSV) over thecatalyst may be from 0.1 to 10 h⁻¹.

The hydrogenation may be carried out in the absence, or preferably inthe presence, of a solvent. Solvents which may be used are any of theliquids which form a homogeneous solution with the starting material andproduct, exhibit inert behavior under hydrogenation conditions, and areeasy to remove from the product. The solvent may also be a mixture oftwo or more substances and, where appropriate, comprise water.

Examples of substances which may be used as solvents are the following:straight-chain or cyclic ethers, such as tetrahydrofuran or dioxane, andalso aliphatic alcohols whose alkyl radical has from 1 to 13 carbonatoms.

Examples of alcohols which may preferably be used are isopropanol,n-butanol, isobutanol, n-pentanol, 2-ethylhexanol, nonanols, industrialnonanol mixtures, decanol, and industrial decanol mixtures, andtridecanols.

If alcohols are used as solvent it can be advantageous to use thealcohol or alcohol mixture which would be produced during saponificationof the product. This prevents any by-product formation viatransesterification. Another preferred solvent is the hydrogenationproduct itself.

By using a solvent it is possible to limit the concentration of aromaticcompounds in the reactor feed, and the result can be better temperaturecontrol achieved in the reactor. This can minimize side-reactions andtherefore increase product yield. The content of aromatic compounds inthe reactor feed is preferably from 1 to 35%, in particular from 5 to25%. In the case of reactors operated in loop mode, the desiredconcentration range can be adjusted via the circulation rate(quantitative ratio of returned hydrogenation discharge to startingmaterial).

The process of the invention is carried out in the pressure range from 3to 300 bar, in particular from 15 to 200 bar, very particularly from 50to 200 bar. The hydrogenation temperatures are from 50 to 250° C., inparticular from 100 to 200° C.

Hydrogenation gases which may be used are any desiredhydrogen-containing gas mixtures in which there are no detrimentalamounts present of catalyst poisons, such as carbon monoxide or hydrogensulfide. The use of inert gases is optional, and is preferable to usehydrogen of purity greater than 95%, in particular greater than 98%.Examples of the inert gas constituents are nitrogen and methane.

Each of the reactors may be supplied with fresh hydrogen. However, inorder to reduce hydrogen consumption and the discharge losses associatedwith the exhaust gas, it is advantageous to use the exhaust gas from onereactor as hydrogenation gas for another reactor. For example, in aprocess carried out in two reactors arranged in series it isadvantageous to feed fresh hydrogen into the second reactor and to passthe exhaust gas from the second reactor into the first reactor. In thisinstance, starting material and hydrogenation gas flow in countercurrentthrough the reactors. It is advantageous for the excess of hydrogen,based on the stoichiometric amount needed, to be kept below 30%, inparticular below 10%, very particularly below 5%.

If nonyl phthalates or mixtures of nonyl phthalates are converted to thecorresponding 1,2-cyclohexanedicarboxylic esters, the hydrogenation ispreferably carried out in the mixed liquid/gas phase or the liquid phasein two reactors arranged in series. The first reactor here is operatedin loop mode, i.e. some of the hydrogenation discharged from the firstreactor is passed together with fresh starting material to the head ofthe first reactor. The rest of the discharge from the first reactor ispassed straight to a second reactor for hydrogenation. It is alsopossible to use two or more relatively small loop reactors instead of alarge loop reactor, these being in a series or parallel arrangement. Itis also possible to operate two or more reactors arranged in series orin parallel with one another instead of a large straight-pass reactor.However, it is preferable to use only one loop reactor and only onestraight-pass reactor.

The process of the invention is preferably carried out under thefollowing conditions:

The concentration of the starting material in the feed of the firstreactor (loop reactor) is from 5 to 30% by weight, in particular from 8to 15% by weight.

The concentration of the starting material in the hydrogenationdischarge from the first reactor is from 0.3 to 8% by weight, inparticular from 1.5 to 4% by weight.

The liquid hourly space velocity over the catalyst (LHSV, liters offresh starting material per liter of catalyst per hour) in the loopreactor is from 0.1 to 5 h⁻¹, in particular from 0.5 to 3 h⁻¹.

The surface area loading in the loop reactor is in the range from 25 to140 m³/m²/h, in particular in the range from 50 to 90 m³/m²/h.

The average hydrogenation temperatures in the loop reactor are from 70to 150° C., in particular from 80 to 120° C.

The hydrogenation pressure in the loop reactor is from 25 to 200 bar, inparticular from 80 to 100 bar.

The concentration of starting material in the starting material for thesecond reactor is smaller than 0.3% by weight, in particular smallerthan 0.1% by weight, very particularly smaller than 0.05% by weight.

The liquid hourly space velocity in the second reactor (liters of nonylphthalate per liter of catalyst per hour) is from 1 to 8 h⁻¹, inparticular from 2 to 5 h⁻¹.

The average temperature in the second reactor is from 70 to 150° C., inparticular from 80 to 120° C.

The hydrogenation pressure in the second reactor is from 25 to 200 bar,in particular from 80 to 100 bar.

The versions of the process are particularly suitable for hydrogenatingphthalic esters, especially for nonyl phthalates (in the form of“isononyl phthalate” isomer mixture, e.g. VESTINOL 9 from OXENO GmbH).

The process of the invention can convert aromatic compounds, such aspolycarboxylic acids and/or monocarboxylic acids or derivatives ofthese, in particular their alkyl esters, to the corresponding alicyclicpolycarboxylic compounds. Either full esters or partial esters can behydrogenated here. Full esters are compounds in which all of the acidgroups have been esterified. Partial esters are compounds having atleast one free acid group (or anhydride group) and at least one estergroup.

If polycarboxylic esters are used in the process of the invention, thesepreferably contain 2, 3 or 4 ester functions.

The aromatic compounds or polycarboxylic esters preferably used in theprocess of the invention are benzenepolycarboxylic,biphenylpolycarboxylic, naphthalenepolycarboxylic, and/oranthracenepolycarboxylic acids, or their anhydrides and/or esters, e.g.alkyl esters having from 2 to 15 carbon atoms. The resultant alicyclicpolycarboxylic acids or derivatives of these are composed of one or moreC₆ rings, where appropriate linked by a C—C bond or fused.

The alcohol component of the aromatic compounds (if those used arecarboxylic esters) is preferably composed of branched or unbranchedalkyl, cycloalkyl, or alkoxyalkyl groups having from 1 to 25 carbonatoms. These may be identical or different within one molecule of apolycarboxylic ester, i.e. the isomers or chain lengths present in acompound may differ. It is also possible, of course, to use a mixture ofisomers with respect to the substitution pattern of the aromatic system,e.g. a mixture of phthalic ester and terephthalic ester.

In one preferred embodiment, the present invention provides a processfor the hydrogenation of benzene-1,2-, -1,3-, or -1,4-dicarboxylicesters, and/or of benzene-1,2,3-, -1,3,5-, or -1,2,4-tricarboxylicesters, i.e. the products comprise the isomers of cyclohexane-1,2-,-1,3-, or -1,4-dicarboxylic esters, or of cyclohexane-1,2,3-, -1,3,5-,or -1,2,4-tricarboxylic esters.

Examples of esters which may be used in the process of the invention arethose of the following aromatic carboxylic acids:

-   naphthalene-1,2-dicarboxylic acid, naphthalene-1,3-dicarboxylic    acid, naphthalene-1,4-dicarboxylic acid,    naphthalene-1,5-dicarboxylic acid, naphthalene-1,6-dicarboxylic    acid, naphthalene-1,7-dicarboxylic acid,    naphthalene-1,8-dicarboxylic acid, phthalic acid    (benzene-1,2-dicarboxylic acid), isophthalic acid    (benzene-1,3-dicarboxylic acid), terephthalic acid    (benzene-1,4-dicarboxylic acid), benzene-1,2,3-tricarboxylic acid,    benzene-1,2,4-tricarboxylic acid (trimellitic acid),    benzene-1,3,5-tricarboxylic acid (trimesic acid),    benzene-1,2,3,4-tetracarboxylic acid. It is also possible to use    acids which are produced from the acids mentioned by using alkyl,    cycloalkyl, or alkoxyalkyl groups to substitute one or more of the    hydrogen atoms bonded to the aromatic core.

Examples of compounds which may be used are alkyl, cycloalkyl, oralkoxyalkyl esters of the abovementioned acids, these radicalsencompassing, independently of one another, from 1 to 25, in particularfrom 3 to 15, very particularly from 8 to 13, particularly 9, carbonatoms. These radicals may be linear or branched. If a starting materialhas more than one ester group, these radicals may be identical ordifferent.

Examples of compounds which may be used in the process of the inventionas ester of an aromatic polycarboxylic acid are the following:

-   nmonomethyl terephthalate, dimethyl terephthalate, diethyl    terephthalate, di-n-propyl terephthalate, dibutyl terephthalate,    diisobutyl terephthalate, di-tert-butyl terephthalate, monoglycol    terephthalate, diglycol terephthalate, n-octyl terephthalate,    diisooctyl terephthalate, di-2-ethylhexyl terephthalate, di-n-nonyl    terephthalate, diisononyl terephthalate, di-n-decyl terephthalate,    di-n-undecyl terephthalate, diisodecyl terephthalate, diisododecyl    terephthalate, ditridecyl terephthalate, di-n-octadecyl    terephthalate, diisooctadecyl terephthalate, di-n-eicosyl    terephthalate, monocyclohexyl terephthalate; monomethyl phthalate,    dimethyl phthalate, di-n-propyl phthalate, di-n-butyl phthalate,    diisobutyl phthalate, di-tert-butyl phthalate, monoglycol phthalate,    diglycol phthalate, di-n-octyl phthalate, diisooctyl phthalate,    di-2-ethylhexyl phthalate, di-n-nonyl phthalate, diisononyl    phthalate, di-n-decyl phthalate, di-2-propylheptyl phthalate,    diisodecyl phthalate, di-n-undecyl phthalate, diisoundecyl    phthalate, ditridecyl phthalate, di-n-octadecyl phthalate,    diisooctadecyl phthalate, di-n-eicosyl phthalate, monocyclohexyl    phthalate, dicyclohexyl phthalate, monomethyl isophthalate, dimethyl    isophthalate, diethyl isophthalate, di-n-propyl isophthalate,    di-n-butyl isophthalate, diisobutyl isophthalate, di-tert-butyl    isophthalate, monoglycol isophthalate, diglycol isophthalate,    di-n-octyl isophthalate, diisooctyl isophthalate, 2-ethylhexyl    isophthalate, di-n-nonyl isophthalate, diisononyl isophthalate,    di-n-decyl isophthalate, diisodecyl isophthalate, di-n-undecyl    isophthalate, diisododecyl isophthalate, di-n-dodecyl isophthalate,    ditridecyl isophthalate, di-n-octadecyl isophthalate, diisooctadecyl    isophthalate, di-n-eicosyl isophthalate, monocyclohexyl    isophthalate.

The process of the invention can in principle also be used on benzoicacid and esters thereof. These include not only alkyl benzoates but alsobenzoates of diols, for example glycol dibenzoate, diethylene glycolbenzoate, triethylene glycol dibenzoate, and propylene glycoldibenzoate. Each alcohol component of the alkyl benzoate may be composedof from 1 to 25 carbon atoms, preferably from 8 to 13 carbon atoms, in alinear or branched structure.

It is also possible to use mixtures made from two or more polycarboxylicesters. Examples of mixtures of this type may be obtained in thefollowing ways:

-   -   a) a polycarboxylic acid is partially esterified using an        alcohol in such a way as to give both full and partial esters.    -   b) A mixture of at least two polycarboxylic acids is esterified        using an alcohol, producing a mixture of at least two full        esters.    -   c) A polycarboxylic acid is treated with an alcohol mixture, and        the product can be a corresponding mixture of the full esters.    -   d) A polycarboxylic acid is partially esterified using an        alcohol mixture.    -   e) A mixture of at least two carboxylic acids is partially        esterified using an alcohol mixture.    -   f) A mixture of at least two polycarboxylic acids is partially        esterified using an alcohol mixture.

Instead of the polycarboxylic acids in reactions a) to f), use may alsobe made of their anhydrides.

Aromatic esters are often prepared industrially from alcohol mixtures,in particular the full esters by route c).

Examples of corresponding alcohol mixtures are:

-   C₅ alcohol mixtures prepared from linear butenes by hydroformylation    followed by hydrogenation;-   C₅ alcohol mixtures prepared from butene mixtures which comprise    linear butenes and isobutene, by hydroformylation followed by    hydrogenation;-   C₆ alcohol mixtures prepared from a pentene or from a mixture of two    or more pentenes, by hydroformylation followed by hydrogenation;-   C₇ alcohol mixtures prepared from triethylene or dipropene or from a    hexeneisomer or from some other mixture of hexeneisomers, by    hydroformylation followed by hydrogenation;-   C₈ alcohol mixtures, such as 2-ethylhexanol (2 isomers), prepared by    aldol condensation of n-butyraldehyde followed by hydrogenation;-   C₉ alcohol mixtures prepared from C₄ olefins by dimerization,    hydroformylation, and hydrogenation. The starting materials here for    preparing the C₉ alcohols may be isobutene or a mixture of linear    butenes or mixtures of linear butenes and isobutene. The C₄ olefins    may be dimerized with the aid of various catalysts, such as protonic    acids, zeolites, organometallic nickel compounds, or solid    nickel-containing catalysts. The C₈ olefin mixtures may be    hydroformylated with the aid of rhodium catalysts or cobalt    catalysts. There is therefore a wide variety of industrial C₉    alcohol mixtures.

C₁₀ alcohol mixtures prepared from tripropylene by hydroformylationfollowed by hydrogenation; 2-propylheptanol (2 isomers) prepared byaldol condensation of valeraldehyde followed by hydrogenation;

-   C₁₀ alcohol mixtures prepared from a mixture of at least two C₅    aldehydes by aldol condensation followed by hydrogenation;-   C₁₃ alcohol mixtures prepared from hexaethylene, tetrapropylene, or    tributene, by hydroformylation followed by hydrogenation.

Other alcohol mixtures may be obtained by hydroformylation followed byhydrogenation from olefins or olefin mixtures which arise inFischer-Tropsch syntheses, in the dehydrogenation of hydrocarbons, inmetathesis reactions, in the polygas process, or in other industrialprocesses, for example.

Olefin mixtures with olefins of differing carbon numbers may also beused to prepare alcohol mixtures.

The process of the invention can use any ester mixture prepared fromaromatic polycarboxylic acids and from the abovementioned alcoholmixtures. According to the invention, preference is given to estersprepared from phthalic acid or phthalic anhydride and from a mixture ofisomeric alcohols having from 6 to 13 carbon atoms.

Examples of industrial phthalates which can be used in the process ofthe invention are products with the following trade names:

-   Vestinol C (Di-n-butyl phthalate) (CAS No. 84-74-2); Vestinol IB    (Diisobutyl phthalate) (CAS No. 84-69-5); Jayflex DINP (CAS No.    68515-48-0); Jayflex DIDP (CAS No. 68515-49-1); Palatinol 9-P    (68515-45-7), Vestinol 9 (CAS No. 28553-12-0); TOTM (CAS No.    3319-31-1); Linplast 68-TM, Palatinol N (CAS No. 28553-12-0);    Jayflex DHP (CAS No. 68515-50-4); Jayflex DIOP (CAS No. 27554-26-3);    Jayflex UDP (CAS No. 68515-47-9); Jayflex DIUP (CAS No. 85507-79-5);    Jayflex DTDP (CAS No. 68515-47-9); Jayflex L9P (CAS NO. 68515-45-7);    Jayflex L911P (CAS No. 68515-43-5); Jayflex L11P (CAS No.    3648-20-2); Witamol 110 (CAS No. 68515-51-5); Witamol 118    (Di-n-C8-C10-alkyl phthalate) (CAS No. 71662-46-9); Unimoll BB (CAS    No. 85-68-7); Linplast 1012 BP (CAS No. 90193-92-3); Linplast 13XP    (CAS No. 27253-26-5); Linplast 610P (CAS No. 68515-51-5); Linplast    68 FP (CAS No. 68648-93-1); Linplast 812 HP (CAS No. 70693-30-0);    Palatinol AH (CAS No. 117-81-7); Palatinol 711 (CAS No. 68515-42-4);    Palatinol 911 (CAS No. 68515-43-5); Palatinol 11 (CAS No.    3648-20-2); Palatinol Z (CAS No. 26761-40-0); Palatinol DIPP (CAS    No. 84777-06-0); Jayflex 77 (CAS No. 71888-89-6); Palatinol 10 P    (CAS No. 533-54-0); Vestinol AH (CAS No. 117-81-7).

It should be pointed out that the ring-hydrogenation of aromaticpolycarboxylic acids or their esters can produce at least twostereoisomeric hydrogenation products from each isomer used. Thequantitative proportions of the resultant stereoisomers with respect toone another depend on the catalyst used and on the hydrogenationconditions.

All of the hydrogenation products with any desired ratio(s) of thestereoisomers with respect to one another may be used withoutseparation.

The present invention also provides the use of the alicyclicpolycarboxylic esters of the invention as plasticizers in plastics.Preferred plastics are PVC, homo- and copolymers based on ethylene, onpropylene, on butadiene, on vinyl acetate, on glycidyl acrylate, onglycidyl methacrylate, on acrylates, or on acrylates having, bonded tothe oxygen atom of the ester group, alkyl radicals of branched orunbranched alcohols having from one to ten carbon atoms, or on styreneor on acrylonitrile, and homo- or copolymers of cyclic olefins.

The following plastics may be mentioned as representatives of the abovegroups:

-   polyacrylates having identical or different alkyl radicals having    from 4 to 8 carbon atoms, bonded to the oxygen atom of the ester    group, in particular having the n-butyl, n-hexyl, n-octyl, or    2-ethylhexyl radical, or isononyl radical, polymethacrylate,    polymethyl methacrylate, methyl acrylate-butyl acrylate copolymers,    methyl methacrylate-butyl methacrylate copolymers, ethylene-vinyl    acetate copolymers, chlorinated polyethylene, nitrile rubber,    acrylonitrile-butadiene-styrene copolymers, ethylene-propylene    copolymers, ethylene-propylene-diene copolymers,    styrene-acrylonitrile copolymers, acrylonitrile-butadiene rubber,    styrene-butadiene elastomers, methyl methacrylate-styrene-butadiene    copolymers, and/or nitrocellulose.

The alicyclic polycarboxylic esters prepared according to the inventionmay moreover be used to modify plastics mixtures, for example themixture of a polyolefin with a polyamide.

The present invention also provides mixtures made from plastics with thealicyclic polycarboxylic esters prepared according to the invention.Suitable plastics are the abovementioned compounds. These mixturespreferably comprise at least 5% by weight, particularly preferably from20 to 80% by weight, very particularly preferably from 30 to 70% byweight, of the alicyclic polycarboxylic esters.

Mixtures made from plastics, in particular PVC, and comprising one ormore alicyclic polycarboxylic esters prepared according to theinvention, may be present in the following products, for example, or maybe used for their production:

-   casings for electrical devices, such as kitchen appliances, computer    cases, casings and components of phonographic and television    equipment, of piping, of apparatus, of cables, of wire sheathing, of    insulating tapes, of window profiles, in interior decoration, in    vehicle construction and furniture construction, plastisols, in    floor coverings, medical products, packaging for food or drink,    gaskets, films, composite films, phonographic disks, synthetic    leather, toys, containers for packaging, adhesive-tape films,    clothing, coatings, and fibers for fabrics.

Besides the abovementioned applications, the alicyclic polycarboxylicesters prepared according to the invention may be used as a component inlubricating oil, or as a constituent of coolants or metalworking fluids.They can also be used as a component in paints, coatings, inks, andadhesives.

The examples below are intended to illustrate the invention withoutrestricting the scope of application defined by description and thepatent claims.

EXAMPLES

The examples below use catalysts which had been prepared from thesupport materials listed in Table 1 together with the physical datarelevant to the invention.

TABLE 1 Properties of supports used Proportion of BET surface areaAverage pore Proportion of pore pore volume in g/m² to DIN diameter dpin volume made up made up by total 66131 (N₂ nm to DIN 66133 Total poreby macropores in of meso- and Material adsorption (Hg porosimetry)volume in ml/g % micropores in % Producer or grade A: TiO₂ 48 34.2 0.46<5 >95 Degussa Aerolyst 7711 B: ZrO₂ 56 25.1 0.29 >55 <45 Degussa H0907C: α-Al₂O non- 7 206.5 0.64 >97 <3 Axence SP 512 inventive

The total pore volume was determined from the total of the pore volumesof pores with dp>7.6 nm (determined using Hg porosimetry) and pores withdp<7.6 nm (determined using the N₂ adsorption method).

Preparation of Hydrogenation Catalysts A, B and, C

To prepare hydrogenation catalysts based on the supports listed in Table1, the supports were first dried at 80° C. After drying, the supportswere impregnated or spray-dried with an aqueous ruthenium(III) nitratesolution which comprised a concentration of 0.8% by weight of ruthenium.

For the impregnation of the support, the Ru nitrate solution was dilutedwith water to a volume corresponding to the pore volume of the support.

The Ru solution was applied dropwise to the support material, orpreferably by uniform spraying while the support is agitated. Afterdrying at 120° C. under nitrogen, the ruthenium-salt-coated support wasactivated (reduced) for 6 hours in a hydrogen/nitrogen mixture (ratio1:9) at 200° C.

Note: In the text below, the resultant catalysts have been indicatedusing the capital letters also used for the underlying support, theactive metal and its content being given in appended brackets.

Hydrogenation Examples 1 to 5

The hydrogenation experiments were carried out in accordance with thefollowing general specification:

90.7 g of the catalyst formed an initial charge in a catalyst basket andwere carefully reduced in accordance with the above specification in thestream of hydrogen in a 1000 ml pressure reactor, and then treated with590 g of liquid diisononyl phthalate (Vestinol 9, OXENO OlefinchemieGmbH). The DINP was hydrogenated using pure hydrogen. Afterhydrogenation of the starting material, the reactor was depressurizedand the reaction mixture was analyzed by means of gas chromatography todetermine its content of target product diisononylcyclohexane-1,2-dicarboxylate (DINCH). This always showed the DINPconversion to be <99.9%.

The experimental conditions for the hydrogenation examples and theresults of these have been entered in Table 2:

TABLE 2 DINP hydrogenation, hydrogenation examples HydrogenationReaction time in Content of DINCH examples Catalyst Starting materialPressure in bar Temperature in ° C. hours in % 1 A (1% Ru) DINP 200 803.5 99.4 2 A (1% Ru) DINP 200 120 1 99.2 3 A (1% Ru) DINP 50 120 2.599.3 4 B (1% Ru) DINP 200 120 2 99.5 5 C (1% Ru) DINP 200 80 20 99.4

Example 6 Hydrogenation of Monoisononyl Phthalate

444 g of phthalic anhydride (3 mol) and 432 g of isononanol (3 mol)(precursors of Vestinol 9) were slowly heated in a round-bottomed flaskwhich has an internal thermometer and a stirrer, and on which a refluxcondenser has been placed. A marked rise in temperature revealed thestart of monoester formation at a temperature of 117° C. Immediatelyafter the temperature rise began, the supply of heat was interrupted.After about 10 minutes the mixture was cooled, having by then reachedits final temperature of about 150° C.

The composition which could be determined by gas chromatography wasabout 95% by weight of monoester, 3% by weight of diester, 0.5% byweight of isononanol, and 1.5% by weight of phthalic acid.

487 g (1.67 mmol, based on pure monoester) of this mixture were mixed,without further work-up, with 240 g (1.67 mol) of isononanol (precursorof Vestinol 9) and charged under nitrogen to a 1000 ml reactor. Afteraddition of 70.7 g of catalyst A (1% Ru) the mixture was hydrogenated at200 bar and 120° C., using hydrogen. Once the ring-hydrogenation of thearomatic carboxylic derivatives had ended, the reactor wasdepressurized. The reactor discharge was transferred into a standardesterification apparatus, mixed with a further 120 g (0.83 mol) ofisononanol and about 0.07 g of tetrabutyl titanate, and esterified understandard conditions to give diisononyl cyclohexane-1,2-dicarboxylate(DINCH).

After removal of the excess alcohol by distillation, and afterneutralization and work-up of the crude product by steam distillation,the purity of the DINCH obtained was 99.4%.

Example 7 Acid-Resistance of a Catalyst of the Invention

A saturated aqueous solution of phthalic acid was hydrogenated in thepresence of catalyst A (1% Ru) at 100° C. and 100 bar to give1,2-cyclohexanedicarboxylic acid. Once the hydrogenation had ended, thesolution was discharged, and reactor and catalyst were flushed withmethanol, isononanol, and DINP. DINP was then again hydrogenated underconditions analogous to Example 2. The hydrogenation was found toproceed with the same selectivities and with at least the same activity.

As can be seen from Table 2, catalysts A and B of the invention areclearly superior in activity to catalyst C.

1. A catalyst for the hydrogenation of aromatic compounds, whichcomprises at least one metal of the eighth transition group of theperiodic table of the elements on or in a support material, wherein thesupport material has an average pore diameter of from 25 to 50 nm and aspecific surface area greater than 30 m²/g, and over 90% of the totalpore volume of the support material is comprised of meso- and microporeswith a diameter of 0.1 to 50 nm, and wherein the catalyst canhydrogenise the aromatic compounds to the corresponding alicycliccompounds.
 2. The catalyst as claimed in claim 1, wherein the supportmaterial comprises activated carbon, silicon carbide, aluminum oxide,silicon oxide, aluminosilicate, titanium dioxide, zirconium dioxide,magnesium oxide, zinc oxide, or mixtures thereof.
 3. The catalyst asclaimed in claim 1, which further comprises at least one metal of thefirst transition group of the periodic table of the elements.
 4. Thecatalyst as claimed in claim 1, which further comprises at least onemetal of the seventh transition group of the periodic table of theelements.
 5. The catalyst as claimed in claim 1, wherein the aromaticcompound comprises benzene-, diphenyl-, naphthalene-, diphenyl oxide-,or anthracenecarboxylic acid, corresponding anhydrides, and/orcorresponding esters.
 6. The catalyst as claimed in claim 1, wherein thesupport material has an average pore diameter of from 25 to 40 nm. 7.The catalyst as claimed in claim 1, wherein the support material has aspecific surface area of from 30-90 m²/g.
 8. The catalyst as claimed inclaim 1, wherein the support material is comprised of meso- andmicropores with a diameter of from 0.1 to 20 nm.
 9. The catalyst asclaimed in claim 1, wherein the content of the metal of the eighthtransition group of the periodic table of the elements on or in asupport material is from 0.1 to 30% by weight.
 10. A process for thecatalytic hydrogenation of an aromatic compound with one or morehydrogen-containing gases on a catalyst which comprises at least onemetal of the eighth transition group of the periodic table of theelements on or in a support material, wherein the support material hasan average pore diameter of from 25 to 50 nm and a specific surface areagreater than 30 m²/g, and wherein over 90% of the total pore volume ofthe support materials is comprised of meso- and micropores with adiameter of from 0.1 to 50 nm, the aromatic compounds comprise aromaticmonocarboxylic acids or their alkyl esters or aromatic polycarboxylicacids or their anhydrides, half esters, or full esters, and saidaromatic compounds are reacted to give the corresponding alicyclic poly-and/or monocarboxylic acid compounds.
 11. The process as claimed inclaim 10, wherein the support material comprises activated carbon,silicon carbide, aluminum oxide, silicon oxide, aluminosilicate,titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxide, ormixtures thereof.
 12. The process as claimed in claim 10, which furthercomprises at least one metal of the first transition group of theperiodic table of the elements.
 13. The process as claimed in claim 10,which further comprises at least one metal of the seventh transitiongroup of the periodic table of the elements.
 14. The process as claimedin claim 10, wherein the aromatic compound comprises benzene-,diphenyl-, naphthalene-, diphenyl oxide-, or anthracenecarboxylic acid,corresponding anhydrides, and/or corresponding esters.
 15. The processas claimed in claim 14, wherein the alcohol components of the esters ofthe organic compounds are in each case identical or different and arealkoxyalkyl, cycloalkyl, and/or alkyl groups having from 1 to 25 carbonatoms, branched or unbranched.
 16. The process as claimed in claim 10,wherein the support material has an average pore diameter of from 25 to40 nm.
 17. The process as claimed in claim 10, wherein the supportmaterial has a specific surface area of from 30-90 m²/g.
 18. The processas claimed in claim 10, wherein the support material is comprised ofmeso- and micropores with a diameter of from 0.1 to 20 nm.
 19. Theprocess as claimed in claim 10, wherein the content of the metal of theeighth transition group of the periodic table of the elements on or in asupport material is from 0.1 to 30% by weight.
 20. The process asclaimed in claim 10, wherein the process is carried out in the pressurerange 3 to 300 bar and the hydrogenation temperature of from 50 to 250°C.